1. Field of the Invention
The present invention relates to a protection technique for protecting a predetermined area on the surface of a substrate.
2. Description of Related Art
Photolithography uses an exposure apparatus which illuminates a mask with exposure light and exposes a substrate with the exposure light from the mask. The mask is provided with a mask substrate (mask blank) and a protective apparatus which protects a pattern area on the surface of the mask substrate. The protective apparatus includes a frame portion, which is called a pellicle frame and is connected to the mask substrate, and a thin film portion, which is called a pellicle and is stretched across the frame portion. An example of a technique related to the mask is disclosed in Japanese Patent No. 4043232.
In the existing mask, the thin film portion deflects as a result of the mask substrate deflecting. Therefore, for example, in a case where the surface of the thin film portion is irradiated with light to detect a surface state (for example, existence of foreign matter), there is a possibility that the irradiation condition of the light and the detection condition of the light may be changed depending on the position of the thin film portion, thereby causing detection errors.